Potentiometer



Mai 19, 1959` A G. MARAsoN, JR 2,387,555

May 19, 1959 G. MARAsoN, JR 2,887,555

l POTENTIOMETER Filed Sept. 9, 1957 2 Sheets-Sheet 2 I 112 ff/ fi neQ/EL Mkmnsaq, Je.,

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United States Patent O POTENTIOMETER Gabriel Marason, Jr., Garden Grove, Calif., Beckman Instruments, Inc., Fullerton, poration of California assignor to Calif., a cor- This invention relates to a potentiometer or the like and, in particular, to improvements in the design of such units which provide more accurate operation in combination with more rugged and durable construction and simpler and less expensive manufacture.

It is an object of the invention to provide a case for a potentiometer or the like in which Van end cover is clamped to the body shell by externally adjustable means not requiring tapped holes or the like in the body shell. A further object of the invention is to provide such a clamping assembly in which the cover may carry a stop which may be rotated relative to the shell Without disassembly of the components. Another object of the invention is to provide such a structure in which a snap ring is rotatably positioned within the shell and is mounted ori the cover by screws or the like for clamping the end of the shell between the snap ring and the cover.

It is another object of the invention to provide a potentiometer or the like in which the rotating block which supports the contact carrier for advancement along the axis of the rotating shaft has a V-shaped groove or shoulder for engagement with mating surfaces of the contact carrier for substantially eliminating mechanical backlash in spite of dimensional errors, wear, temperature changes and the like. A further object of the invention is to provide such a structure in which the stop-engaging surfaces of the contact carrier are parallel to the mating surfaces of the rotor block and contact carrier.

It is a further object of the invention to provide a potentiometer or the like having a slip ring which can be formed of a single flat piece of material with a terminal lug extending radially outward from the case and with resilient, peripheral ears or tabs engaging the mounting shoulder in the end of the case. Another object of the invention is to provide a potentiometer or the like in which the rotor block carried on the shaft is of open rectangular construction permitting the pigtail lead from the slip ring contact to the coil contact to be restrained within the frame and protected from relatively moving parts. A still further object of the invention is to provide a potentiometer construction which permits provision of long electrical leakage paths between components at different electrical potentials.

While the invention will be described herein in conjunction with a helical potentiometer, it will be seen that certain features of the invention are equally applicable to other electrical components having rotating and iixed elements mounted within a case. The invention also comprises novel details of construction and novel combinations and arrangements of parts, which will more fully appear in the course of the following description. The drawings merely show and the description merely de-` scribes a preferred embodiment of the present invention which is given by way of illustration or example.

In the drawings:

Fig. 1 is a longitudinal sectional view of a preferred embodiment of the invention;

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Fig. 2 is a sectional view taken along the line 2 2 of Fig. l;

Fig. 3 is a sectional view taken along the line 3 3 of Fig. l;

Fig. 4 is a sectional view taken along the line 4 4 of Fig. l;

Fig. 5 is a sectional view taken along the line 5 5 of Fig. l;

Fig. 6 is a partial sectional view taken along the line 6--6 of Fig. 5;

Fig. 7 is a partial sectional view taken along the line 7 7 of Fig. 4;

Fig. 8 is a partial sectional view taken along the line 8 8 of Fig. 4;

Fig. 9 is a partial sectional view taken along the line 9 9 of Fig. 3;

Fig. 10 is an enlarged plan view of the contact carrier of the embodiment of Fig. l; and

Fig. 11 is a sectional view taken along the line 11 11 of Fig. 10.

The potentiometer illustrated herein has a case 20 comprising a shell 21 and a cover Z2, the shell preferably being formed of an electrical insulating material. A helical coil 23 is fixed in a helical groove 24 in the internal surface of the shell 21, the coil preferably comprising a core 25 formed as a major helix with a resistance wire 26 wound on the core as a minor helix. Terminal assemblies 27, 28 are xed in the shell 21 providing for external connections to the coil within the shell` Each of the terminal assemblies includes an insert 30 which is pressed into an opening 31 in the shell, a U-shaped llug 32, and a hollow screw 33 for clamping the lug to the insert. A wire may be passed from the coil within the shell through the hollow screw and soldered to one of the eyes of the lug.

An inwardly turned shoulder 36 at the open end of the shell 21 defines an annular groove 37 in which a ring 38 is rotatably positioned (Figs. 1 and 5). A preferred form for the ring 38 is shown in Fig. 5, the ring being a conventional internal snap ring having an opening 40 at each end thereof for engagement by a compressing tool to compress the ring for insertion into the internal groove 37. Three equally spaced threaded openings 41 are also provided in the ring 38.

The cover 22 is constructed to rotatably engage the open end of the shell 21, the cover preferably having a section 44 which projects into the zone enclosed by the shoulder 36 of the shell, means being provided for clamping the ring 38 to the cover with the shoulder 36 between the ring and cover. Screws 45 may be positioned in counterbored openings 46 in the cover for threading into the openings 41 in the ring, advancement of the screws drawing the ring and cover toward each other with the shoulder therebetween. Thus, after the case has been assembled, the relative positions of the shell and cover may be adjusted by slightly loosening the screws 45, rotating one element relative to the other, and then tightening the screws. Rapid and accurate phasing of shell and cover is thereby accomplished without the necessity of disassembling the unit or of providing threaded openings in the shell itself. Such cover-shell assembly may be used at either or both ends of the case if desired.

The case 20 of the invention may be mounted on a panel 49 by positioning a projecting portion 50 of the cover 22 in an opening 51 in the panel and clamping the cover to the panel With brackets 52 which engage a shoulder 53 of the cover. With this type of mounting, the angular position of the shell relative to the cover and panel can be adjusted without disturbing the mounting of the case to the panel.

Alternatively, the case may be mounted to a panel 56 by positioning the projecting portion 50 of the cover in a recessed section 57 of the panel and usingk screws 5S passing through openings 59 in the panel and the openings 46 in the cover for engaging the ring 38.

A shaft 62 is mounted'in the case'Z for rotation'vabout vthe axis of the helical coil 23 by a bearing 63 mounted Vin vone end 64u of the caseanda bearing'65 mounted in the cover 22, the bearing 65, the shaft and the cover being'held `together by an internal snap ring 66 and an external snap ring 67.

A rotor `block'70 ismounted on the shaft 62 'for' rotation therewith and a contact carrier 71 rides on the rotor `block for movement substantiallyv parallel to Ithe axis of rotation of the shaft, the contact carrierincluding means for engaging the turns of thehelicalcoil to advance the carrier along the rotor block as the shaft'is rotated. The

rotor blockL is'preferably formed as an open rectangle as seen in Fig. l with parallel members 72"and 73'spaced fromthe shaft 62 and parallel members`74 and '7S having aligned openings therein for receiving the shaft, the rotor block being xed to the shaft by a roll pin" 76 in aligned openings in theshaft and member 75.

VThemember '72 of the rotor block has flat walls 79, 80 which lie in planes that intersect at a line substantially parallel to the axis'of the shaft 62. The contact`carrier 71 has corresponding flatwalls 81, 82 (Fig.

ll) for surface engagement with the'walls of the memvber 72. The walls 79 and 80 of the member 72 serve as a guide groove for the contact carrier and preferably converge toward the shaft which carries the rotor.

-A 'exible contact S5 for electrically engaging the turns of the helical coil is carried on the contact carrier 71'by suitable means, such as by spot-welding the contact to a conducting-strip 86 which is-xed to the contact carrier 71 by a rivet S7 (Figs. l0 and 1l). A preferred construction for the guiding engagement between the contact carrier and the turns of the helical coil includes parallel ribs 38,' 89 of insulating material extending outward from the contact carrier for engaging the sides of the turn which is being electrically contacted by the contact 85. The'ribs'88, 89 are preferably skewed to the helix angle of the major helix for better alignment with the -turns of the coil (Fig.

When the contact carrier is positioned in the guide groove of the rotor block with the flexible contact engaging a turn of the coil as'seen in Fig. l, the exible contact urges the walls 81, 82 of the contact carrier and the walls 79, 80 of the guide groove into engagement.

`Since the planes of'these walls converge at thesame angles, Vthe contact carrier will always engage the rotor Y block without mechanical .backlash or lateral play along 'the axis of the minor: helix and this .desirediit will be maintained without binding even though the components are'subjected to extreme operationand wear and extreme temperature ranges.

Stops are ordinarily provided in helical ypotentiometers and Vsimilar units for limiting thetravel of the 'contact along the turns'of .theihelical coil. In the Ystructure shown herein,l a .pin 92.isv mounted in and projectsin- Ward from .the cover/2tev serve asone stop and a boss 93.'is formed in the end 64 of theI case to serve as the otherstop. Stop-engaging surfaces94 and 95.. are providedon vopposite sidesrof Vthe. contact carrier' 71, .the stop-engaging'surfacel beingparallel to thewall 81 vand the surface 59S 'beingparallel to .the wall'82. At

one extremey of travel, L' the? surface 95 will engage the boss 93.and at the otherextreme of travel, thesurface 94 'will rengage the pink 92. YBecause of .the parallel rela- ;tionzofthe. surfacesfiothe contactcarrienthelaction of the stopsis positiveY Withfno movement of the contact .carrier relative tothe rotor blockor rto the helical coil V.when aistop is engaged,lthus eliminating another source ofrnechanical backlash. A'stronger structure `also results from this construction, since .the forces'exerted at z stopengagernent u are Vin 1. compressionf` ratherl than shear.

The angular adjustment of cover and shell previously described, permits the exact position of the'stops to be set after the unit has been assembled, since the stop 92 is mounted in the cover.

External electrical connection is made to the sliding contact through a slip ring 98, a slip ring wiper 99 and a flexible lead 100. .The slip ring 98 includes an elongated tongue 161, an annular section 102 and four ears or tabs 103 extending outward from the periphery of the annular section 102. The slip ring is preferably made from a single at piece of electrically conducting metal and is mounted in the base by passing the tongue 101 outward through a radial slot 194 in the shell 21 and Vthenpressing the annular section 192 into the space enclosed by an annular shoulder 165 in fthe end 64 of the case, the ears 103 extending inwardly (Figs. l and 7) and engaging the inner surface of the shoulder 105 and fixing the slip ring in position. A channel 106 is preferably'formed in the tongue 101 intermediate the ends thereof to make the tongue a push t in the slot 104. The channel portion of the tongue effectively closes the slot and also raises the resonant frequency ofthe structure thereby reducing the sensitivityvof the slip ring assembly to vibration.

The slip ring wiper 99 includes a block ltl'of insulating. material mounted on the rotor block 7) adjacent the member 73 with a screw 109, a'conducting'strip 110 molded in the block 10S, and a spring contact 111 soldered totheconducting strip, the contact including a pair of iingers 112having contact points 113 thereon for engaging a path on theslip ring 98 concentric with the shaft 62. LOneend of the exible llead lll() is soldered to the con- 'ducting strip '110 of the slip ring wiper and the other end rotor block at the slip ring wiper, through the open rotor block audaround the shaft to the other side of the rotor block at the contact carrier, as seen in Figs. l, 2 and 3. Thus, while the contact carrier moves from one end to .the other of the rotor block, the flexible lead is maintained within the confines of the rotor block and is kept from coming into accidental Contact with the coil or case.

By utilizing the construction disclosed herein, it is possible Vto obtain long current leakage paths between elements of the unit which are operated at different electrical potentials so that the leakage paths have high resistance and highbreakdown potentials. For example, the slip ring wiper block 168, which is mounted ata corner of the rotor Vblock by a single screw, may be providedV with long skirts .116 of insulating material wrapping around the 'rotor block and providing a long path between the conductor strip 110 and the rotor block. Similarly, the contact carrier 71 may include flanges 117 extending over the the contact carrier and the rotor block. For the same reason, the slip ring 98 may be positioned in an annular recess of the end 64 of the case with a long shoulder 118 separating'the slip ring from the bearing 63 (Fig. l).

Although an exemplary embodiment of the invention has been disclosed and discussed, it will be .understood that other applications of the invention are possible and that the embodiment disclosed may be subjected to vari- F ous changes, modifications and substitutions without necessarilydeparting from the spirit of the invention.

I claim.as myy invention:

yl. Ina case for ak potentiometerV or the like, the combination of: acylindrical `shell having an inwardly turned peripheral shoulder defining an inwardly opening annular groovein. said .shelland a` circular opening at one end thereof; a detachable cover rotatable in said circular opening about the axis of said shell; a ring positioned in said groove for rotation relative to saidshell with said shoulder retaining said ring within saidshell; and vmeans forxing said cover to said ring to clamp said shoulder between said cover and ring.

2. In a case for a potentiometer or the like, the combination of: a cylindrical shell having an inwardly turned peripheral shoulder defining an inwardly opening annular groove in said shell and a circular opening at one end thereof; a cover for engaging said one end of said shell with a portion of said cover disposed within said opening for positioning said cover relative to said shell; a split ring positioned within said groove for rotation relative to said shell, said ring being temporarily compressible from its normal diameter to a smaller diameter to pass through said opening defined by said shoulder, with said shoulder retaining said ring within said shell when said ring attains its normal diameter; and means for fixing said cover to said ring to clamp said shoulder between said cover and ring.

3. yIn a case for a potentiometer or the like, having a rotating element disposed within the case, the combination of: a cylindrical shell having an inwardly turned peripheral shoulder defining an inwardly opening annular groove in said shell; a cover for positioning at one end of said shell in engagement with said shoulder, said cover being rotatable relative to said shell about the axis of said shell; a stop member carried on said cover and projecting into the interior of said shell for engagement with a portion of the rotating element; a ring positioned in said groove for rotation relative to said shell with said shoulder retaining said ring within said shell; and means for fixing said cover to said ring to clamp said shoulder between said cover and ring, said cover and ring being rotatable together relative to said shell when said last mentioned means are temporarily loosened.

4. In a case for a potentiometer or the like suitable for mounting to a plate, the combination of: a cylindrical shell having an inwardly turned peripheral shoulder de- -ning an inwardly opening annular groove in said shell;

a cover having a first surface for engaging said shoulder and a second surface for engaging the mounting plate, said cover being rotatable relative to said shell about the axis of said shell, said cover having a plurality of mounting openings therein substantially parallel to said axis; a ring positioned in said groove for rotation relative to said shell with said shoulder retaining said ring within said 1 shell, said ring having a plurality of threaded openings in alignment with said mounting openings in said cover; and

a plurality of screw means for passing through the mounting plate and said mounting openings in said cover and threadedly engaging said openings in said ring for clamping said cover and shoulder between the mounting plate and said ring.

5. In a potentiometer having a helical coil positioned within a case and a shaft mounted in the case for rotation about the axis of the helix, the combination of: a rotor carried on the shaft and including a carrier guide, said guide having a pair of ilat walls disposed substantially parallel to the shaft with the planes of said walls intersecting at an angle along a line parallel to said guide; a contact ycarrier having a pair of flat walls lying in planes which intersect at an angle substantially equal to the angle of intersection of the planes of said walls of said guide, for engagement with said carrier guide and movement therealong; and a spring contact mounted on said carrier for engagement with a turn of the coil, said contact urging said carrier into engagement with said guide, inhibiting movement of said carrier except in a plane substantially parallel to the shaft, said carrier including means for engaging the sides of the turns for advancing said carrier along said guide as the shaft and rotor rotate.

6. In la potentiometer having a helical coil positioned Within a case and a shaft mounted in the case for rotation about the axis of the helix, the combination of: a rotor carried on the shaft, said rotor having a guide groove therein `disposed substantially parallel to the shaft, the opposing walls of said groove converging toward the shaft; a contact carrier for engagement with and movement along said rotor, said contact carrier including a portion mating with and resting on said converging walls of said guide groove; and a spring contact mounted on said carrier for engagement with a turn of the coil, said contact urging said portion of said carrier into engagement with said guide groove of said rotor, inhibiting movement of said carrier except in a plane substantially parallel to the shaft, said carrier including means for engaging the sides of the turns for advancing said carrier along said groove as the shaft and rotor rotate.

7. In a potentiometer having a helical coil positioned within a case and a shaft mounted in the case for rotation about the axis of the helix, the combination of: a rotor carried on the shaft and including a carrier guide, said guide having a pair of flat walls disposed substantially parallel to the shaft with the planes of said walls intersecting at an angle along a line parallel to said guide; rst and second stops fixed to opposite ends of the case and projecting inward toward each other; a contact carrier having a pair of iiat walls lying in planes which intersect at an angle substantially equal to the angle of intersection of the planes of said walls of said guide for engagement with said carrier guide and movement therealong; and a spring contact mounted on said carrier for engagement with a turn of the coil, said contact urging said carrier into engagement with said guide, inhibiting movement of said carrier except in a plane substantially parallel to the shaft, said carrier including means for engaging the sides of the turns for advancing said carrier along said guide as the shaft Iand rotor rotate, said carrier including a first stop-engaging surface on one side thereof disposed parallel to one of said flat walls for engaging one of said stops providing a limit on the travel of said carrier along said guide, and including a second stop-engaging surface on the opposing side disposed parallel to the other of said at walls for engaging the other of said stops providing a second limit on the travel of said carrier along said guide.

8. In a potentiometer having a helical coil positioned within a case and a shaft mounted in the case for rotation about the axis of the helix, a combination of: a rotor comprising an open rectangular frame mounted on the shaft for rotation therewith, said frame including parallel members disposed on opposite sides of the shaft and spaced therefrom, one of said members having a guide groove therein disposed substantially parallel to the shaft with the opposing walls of said groove converging toward the shaft; a contact carrier for engagement with and movement along said one member, said contact carrier including a portion mating with and resting on said converging walls of said guide groove; a spring contact mounted `on said carrier for engagement with a turn of the coil, said contact urging said carrier into engagement with said guide groove, inhibiting movement of said carrier except in a plane substantially parallel to the shaft, said carrier including means for engaging the sides of the turns for advancing said carrier along said groove as the shaft and rotor rotate; an electrical terminal insulatedly mounted on the other of said member; and a flexible electrical lead interconnecting said terminal and said contact, said lead passing from said terminal on one side of said other member, through said frame and around said shaft to said contact on the opposite side of said one member.

9. In a potentiometer or the like, the combination of: a case; a helical coil positioned within said case; a shaft mounted in said case for rotation about the axis of said helix, said case having an inwardly projecting shoulder in one end thereof concentric with said shaft and a radial slot in the side Wall thereof adjacent one end; a rotor comprising an open, rectangular frame mounted on said shaft for rotation therewith, said frame including :assauts .parallel niemlryers .disposed onoppositetsides ofi said ".shaftand spaced:therefrom,z.one of said members having a guidegroovetherein disposed-:substantially parallel to.said..shaft, .the opposing Walls.ofsaidfgroove;con

verging toward said shaft; a contact carrier for engagementtwithand movement along said one'member, said contact Ycarrier .including a portion mating with and resting on said converging walls of saidguide: groove; aspring contact mounted on said carrier for engagement with a turn of said coil, said contact urging saidicarrier :into engagement with said guide groove, inhibitingmovement of said carrier except in a plane .substantially parallel to the shaft, said carrier including means for engaging .the sides of the turns for advancing said carrier along said guide vgroove as said shaft and lrotor rotate;

an. electrical terminal insulatedlyi-mounted ontheother of `said members; a flexible electrical lead. interconnecting said terminal and said.contact,. said lead vpassingfrom said terminal on one side. ofsaid other member, through said .frame and around said shaft to said contact .on-v vthevopposite side of said one member; .and a slip .ring kcomprising a unitary.' piece of electrical conductingimetal,

said slip ring .including anelongated .tongue section, an apertured flat. section, 'and a.plurality of .resilient Vtabs extending outwardfromsaid .ati section,..said tongue section extending throughsaid radialv slotto the exterior of-said case and said. flat sectionbeingzdisposed within said lshoulder around' said shaft with said tabs urged outward into engagement with said shoulder, said terminal including a flexible contact for riding on said at section as said'shaft rotates.

10; In a potentiometer orthe like Ahaving an electrical component arcuately disposed withiny a `case with a rotating shaft carrying `an electrical contact for engaging various portions of the electrical .componentfas vthe shaft'- rotates, the combination of: a shoulder on .oneend of the case projecting into the interior :of the case and including a concave zone concentric with the. shaft;

vmeans dening aradial `slot through the uwall of the vof said slip ring as .the shaft rotates.

i8 11..;In z at case: for a potentiometer or ,theixlike, gthe combination of: a cylindrical shell havingy aninwardly .turned peripheral'shoulder delining Tan inwardlypopening annular groove in` said .shell and a'circularopeningzat onel end thereof; a ,detachable cover-.rotatable in'eaid circularopening about the axis of said shell, said'zcover including a stop member integral therewith and extending into .the interior of said shell for rotation about .said axis;l aring positioned in said groove for rotation relative ,to said shell with the outside diameterof saidring greater `than the diameter of said circular openingsuch that said shoulder retains said ring'withinsaid shell; and meansfor ixing said cover to said ring to clamp said .shoulder between said `cover and ring.

12. Ina case for a potentiometer or the likesuitable for;mounting to a plate, .the case Yhaving afrotating element disposed therein, the combination of: acylindrical shell having an vinwardly turned .peripheral shoulder Vdefining an inwardly opening annular .groove .in said shell; a cover having a first surface for; engaging said. shoulder and a second surfacefor engaging. .the

.mounting plate, said cover being rotatable relative to said shell aboutthe axis of said shell, said` cover/.having .a vplurality of mounting openings therein `substantially :parallel to. said axis; a stop member' fixed to saidshell and rotatable therewith for engagement with a portion of therotating element; a split ring positionedwithn said groove for rotation relative to `Saidy shell, said ring being temporarily compressible from its normal ydiameter to a'v smaller diameter to pass through said openingdened by said shoulder, with said shoulderv retaining'said: ring Within vsaid .shell when 4saidring attains its;normal diameter, said ring having a plurality .of threaded openingsin alignment with said mountingopenings in said cover; and afplurality of screws for passing :through the .mounting plate and said mounting openingsV insaid cover and threadedly engaging saidopenings in saidring for clamping said cover andvsaid shoulder betweenthe mounting plate .and said ring.

. References Cited inthe file of this patent UNITED STATES APATENTS 2,473,048 Beckman lune.v 14, :1949 I 2,495,321 Gibbs et al. Jan; 24,1950 2,519,752 Fox Aug..22, 1950 2,558,326 -Van Dyke Iune'26,'1951 .2,665,355 Van Alen et al. Ian. 5, 1954 2,813,182 Van Alen Nov. 12,1957 

